This invention concerns polymers and paints. More particularly it concerns polyester-epoxy polymers filled with carbon black and particularly suited for use as electrically conductive coating compositions for use on automobiles, including nonmetallic parts.
The present invention is an adaption of and improvement over that of U.S. application Ser. No. 613,413 (FF-7795), Huybrechts, Meeus and Timmerman, filed May 24, 1984, now U.S. Pat. No. 4,602,053, the disclosure of which is incoporated herein by reference.
Coating systems for automobiles normally comprise a multiplicity of coatings applied to substrates of steel and sometimes also other materials, including electrically non-conductive organic-based composite materials. Typically, the steel is treated with a phosphate, than a cathodic electrocoat primer is applied. A primer-surfacer is used next to smooth the surface and provide a thick enough coating to permit sanding to a smooth, flat finish. Then a topcoat system is applied, sometimes as a single colored coat, often as a basecoat with solid color or metallic pigments followed by a clear coat.
When a non-conductive material is used for part of a car body, it is important to provide an electrically-conductive coating over it so that when the topcoat paint is applied electrostatically to the entire car, a uniform appearance will be produced. Among such non-conductive materials are reaction injection molded (RIM) parts and various fiberglass filled composites.
It is difficult to find a paint that can be made adequately conductive for such applications while still being tough and flexible enough to be a useful paint.